INVESTMENTS (Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Available-for-sale Securities, Debt maturities, Amortized cost:
One year or less	$ 34,393	$ 46,189
Over one through five years	177,620	177,982
Over five through ten years	161,961	150,557
Over ten years	1,215	1,916
Amortized cost	375,189	376,644
Available-for-sale Securities, Debt maturities, Fair value:
One year or less	34,469	46,231
Over one through five years	178,374	177,899
Over five through ten years	161,955	148,783
Over ten years	1,172	1,843
Fair value	375,970	374,756
Held-to-maturity Securities, Debt maturities, Amortized cost [Abstract]
One year or less	184	170
Over one through five years	1,763	1,719
Over five through ten years	3,541	3,662
Amortized cost	5,488	5,551
Held-to-maturity Securities, Debt Maturities, Fair value:
One year or less	185	170
Over one through five years	1,795	1,750
Over five through ten years	3,451	3,553
Fair value	5,431	5,473
Total Investments [Abstract]
Amortized cost	380,677	382,195
Fair value	$ 381,401	$ 380,229